swallow, gulp down, greedy
噲 centers on taking something in quickly and completely: swallowing, gulping down, or acting with greedy haste.
噲 combines 口 (mouth) with 會, which likely contributes the sound and the idea of gathering or meeting, suggesting a mouth gathering and swallowing food or drink.
A mouth 口 beside 會 (meeting/gathering) suggests a mouth gathering everything in at once: swallowing greedily.
For カイ, imagine a greedy person swallowing a whole pie in one gulp: pie -> カイ, and the mouth 口 on the left gulps it down.